Electrically illuminated signboards used for advertisement in stations or the like have a structure, as shown for example in FIG. 8, in which several straight fluorescent lamps (hereinafter referred to as fluorescent lamps) 101 or the like are arranged in a light reflection casing (housing) 102 so as to irradiate a display panel 104 or the like through a light diffusion plate 103 or directly. The housing is formed of, for example, stainless steel, aluminum or the like in a shape of a box having an opening at a top surface side, and the fluorescent lamps 101 or the like are provided therein. Then, the housing is formed by coating a light reflection material inside so that light from the fluorescent lamps irradiates the display panel 104 provided at a front side without being wasted (cf. for example PATENT DOCUMENT 1 (FIG. 9)).
On the other hand, as a surface light source using semiconductor light emitting devices (hereinafter referred to as LEDs, too), there has been introduced the surface light source irradiating light from the LEDs to a front side by introducing from a side face of a light guide plate and reflecting by a reflection plate provided at a back surface of the light guide plate or the surface light source formed by arranging LEDs, directly under the light diffusion plate, on the back surface of the light guide plate or without using the light guide plate (cf. for example PATENT DOCUMENT 1 (FIG. 7)).    PATENT DOCUMENT 1: Japanese Patent Application Laid-Open No. 2003-330394